Video: Lawmakers fume over gas testing methods

We've all seen them — those estimated gas mileage numbers posted on new cars. Numbers that turn out to be phony, according to the American Automobile Association (AAA), which has released its own set of numbers for consumers.

"I'm sure they take it downhill with the wind behind you to make it sound good," says another.

There are some huge differences between the EPA mileage estimates and the AAA numbers. For instance, a BMW Z4, rated at 21 miles per gallon city and 29 highway by the EPA gets only 14.5 miles per gallon in the AAA tests.

The popular Chrysler PT Cruiser, also rated at 21 city and 29 highway by the EPA, got a AAA average of 17.5 miles per gallon.

And the GMC Sierra, with an EPA rating of 16 city and 21 highway, got an auto club number of 15.3 miles per gallon.

The problem, says AAA, is that the federal government does not test cars in real world situations and doesn't factor in things like running the air conditioner or driving in stop-and-go traffic. Most tests are conducted in labs with the engines already warmed up, the speed kept below 60 miles an hour.

Now, two members of Congress have introduced legislation to change EPA testing methods.

"They have a statement that says, 'your actual mileage may vary,'" says the bill's co-author Rep. Rush Holt, D-N.J. "They should say, 'your actual mileage bears no relationship to these numbers in the window.'"

The EPA released a printed statement saying it's re-evaluating its fuel economy calculation to provide consumers with more realistic information. The idea: To eliminate that other kind of sticker shock, when you find your new car doesn't measure up to the government's mileage figures.